Herbivory, climate change and the future landscape of Isle Royale National Park: developing an herbivory monitoring program to adaptively manage the park’s terrestrial and aquatic ecosystems
Background: Isle Royale National Park and Biosphere Reserve is an island archipelago in Lake Superior and home to a dynamic predator-prey relationship (wolf-moose), studied for over 50 years. The landscape is also dynamic, with a portion of the island at the northern edge of the temperate forest zone, and a portion at the southern edge of the boreal forest, making it particularly vulnerable to changing climate. Moose arrived on Isle Royale in the early 1910s, and altered the island forest vegetation through heavy browse. Moose populations grew to 2000-4000 in the late 1920s, then collapsed due to starvation and harsh winters. The population recovered after a large wildland fire stimulated forest regeneration. In the 1940s wolves arrived via an ice bridge from Minnesota, and established on the island as the sole predator of moose. Moose and wolf populations have since fluctuated, with moose browse continually exerting pressure on vegetation. In the past 5 years the wolf population has plummeted, and as of the winter of 2016 was estimated to be 2 individuals. Meanwhile, the moose population is growing at rate of roughly 20% annually, and was estimated at 1,300 in early 2016. A decision is forthcoming on whether the park will reintroduce wolves to the island to maintain predation as a community dynamic on Isle Royale (https://parkplanning.nps.gov/projectHome.cfm?projectID=59316). However, it is expected in the short term with no predator pressure, the moose population and associated herbivory impacts will continue to grow.
On Isle Royale, herbivory and its effects have played a large role in shaping the island ecosystem. Moose are dependent on vegetation for food and cover, and can influence the characteristics of vegetation (e.g., species composition, spatial heterogeneity) as much as they are influenced by it (Pastor et al. 1988). Estimates of biomass removal by moose on Isle Royale range from 0.1 to 25 kg/ha-1/yr-1 (McInnes et al. 1992) and represents less than 3% of annual shrub and sapling production. An important factor in determining effects of moose herbivory is the rate at which plants recover from herbivore-inflicted damage. Herbaceous and aquatic vegetation may recover from herbivory relatively quickly, however, shrubs and saplings possess slower growth rates, and growing shoots are preferentially removed; thus, the functional groups typical of forests may be disproportionately affected by moose herbivory (McInnes et al. 1992). In boreal forest succession, spruce and balsam fir commonly replace short lived aspen and paper birch. However, browse of balsam fir and changing climate have led to community shifts in vegetation; since the 1950s, boreal forest cover on Isle Royale has declined from 72% to 53% and northern temperate forest cover has increased by almost 15% (Kraft et al. 2010). The formation of moose-spruce savannas (Rotter and Rebertus 2015) and transition to northern temperate species will alter the fundamental character and function of island forest ecology.
Moose are also not the only herbivore on Isle Royale. Beaver and snowshoe hare also reside on Isle Royale. Their impacts, while considerably less than moose, are likely to have synergistic impacts alongside moose. It will be important for NPS management to consider the full impacts of herbivory on Isle Royale to allow for adaptive management in the context of climate change.
Project Goals: The goal of this project is to develop a comprehensive monitoring program to assess the long-term impacts of herbivory on seedling recruitment, forest composition, understory plant communities and aquatic plant communities at Isle Royale National Park. Cascading ecosystem effects of herbivory and species shifts can include changes in soil fertility, decreased tree biomass production, and increase competition for resources important to other wildlife dependent on browsed species. In addition, future climate conditions may decrease the boreal forest species that are preferential moose forage.
Justification: Herbivory, and its associated impacts, have been studied since the 1930s, however Isle Royale National Park still lacks a comprehensive program to monitor for herbivory across the island, assess forest and aquatic vegetation community changes and make future projections on forest composition, especially in the context of climate change. Much of the forest land on Isle Royale is at the southern extent of the boreal forest range and key tree species of this ecosystem are preferential forage for the suite of herbivores and thus, not regenerating. It is vital to understand ecosystem response to both herbivory and climate change to inform future park management. In addition, it will be beneficial to have an inventory and monitoring program established in the wake of a park management decision on the wolf population.
Specific activities and duration: Given the project scope, it is reasonable to estimate the activities outlined below will take 14-16 months for a team of 3-4 students.
- Compile extensive review of past forest and vegetation monitoring activities and vegetation characteristics
- Conduct a climate change vulnerability assessment for terrestrial and aquatic environments impacted by herbivory
- Evaluate and summarize results of previous and existing monitoring approaches, current status of the island’s forest and aquatic communities, and community changes since the early 1900s
- Evaluate herbivory impacts to aquatic communities and potential monitoring approaches to include remote sensing
- Create a monitoring plan for assessing herbivory impacts and associated changes in terrestrial and aquatic communities, which incorporates forecasted climate change impacts and accounts for the interplay between the moose population, the terrestrial and aquatic environments and climate change.
Integrative approach: This is a complex project, and involves communication with and an understanding of the National Park Service, development of robust protocols aimed towards long-term management, extensive literature review and analysis of historical data, use of GIS and development of a geodatabase, and climate change considerations (e.g. adaptation strategies) in long term monitoring and planning efforts. We envision this project to involve team members interested in ecosystem ecology, geographic information systems, soil biogeochemistry, wildlife management, public lands management and communications. Additionally the team of students could partner with the Northern Institute of Applied Climate Sciences and the National Park Service to provide a climate vulnerability assessment for the park. This would allow the students to work directly with natural resource management professionals, federal land managers and climate scientists in an integrative process to solve help solve a real management issue greatly impacted by climate change and achieve the projects goals outlined in this proposal.
Margaret Lindman Mirko Noack Robin Schultze Jordon Tourville Charlotte Weinstein